Excel 2003 :: Get Dates To Remain In Consistent Format

I have been struggling to get dates to remain in a consistent format within my Excel 2003 worksheets. I would like to work out how to keep them permanently in the "dd/mm/yyy" format. I have tried several formatting options. The current method I will explain below:

I have several forms into which the 'date' is automatically entered using the - Format(Date, "dd/mm/yyyy") code. This is then saved into cells on a worksheet using the code

ws.Cells(iRow, 1).NumberFormat = "dd/mm/yyyy"
ws.Cells(iRow, 1).Value = CDate(Me.Date1.Caption)

At this point if I do a search for a date, lets say 23/03/2012 I can retrieve it and everything related to it - all seems fine (also all dates are visually in the correct format in my cells etc).

The problem arises when I exit Excel and save the workbook. When I go back into the workbook at a later time and try and search for the same date it won't work. Although the dates in the cells still read for example 23/03/2012, the search requires me to now use the format 03/23/2012 to retrieve the information (It seems like in the background the date has reverted to the US date format upon saving and yet visually it is still how I've set it up).